Lecture 26: Equine Anesthesia (Exam 4) Flashcards
Describe general fasting for equine
Generally with hold food 3 to 6 H so horse is not overly stressed
What should be considered w/ equine ax
- Safety first
- Behavior is complex
- Are prey animal so everything looks scary to them
- Adequate staff & facilities to be able to handle it
- Increased risk of ax in horses (1.9% mortality rate)
What are the anatomy & physio considerations
- Obligate nasal breathers (the position they are in can cause edema of the nasal passages)
- Prone to V/Q mismatch & hypoxemia
- GI Tract considerations
- Large muscle mass & body weight (Dev myopathy &/or neuropathy)
What increase risk in equine
- Fracture repair
- Younger (< 1 m) or older ( > 14 Y)
- Colic & or emergency
- Sx btw/ midnight & 6 am
- Experience of surgeon
- Duration of ax
- Trauma, dehydration,, stress, general poor condition, & systemic dx
- Preg
- Drug choices
- Breed predisposition
What is chariot
Newer tool to use in the pre ax assessment of risk that augments the ASA physical status sys by accounting for additional factors unique to equine px
Describe respiratory consideration
- Prone to compression atelectasis when placed in dorsal recumbency
- All ax drugs depress respiratory drive, muscle fxn, ventilatory rate & volume, & the response to hypercarbia & hypoxia
- Inhalant ax alter the distribution of pulmonary flow by abolishing hypoxic pulmonary vasoconstriction
- Upper airway obstruction from nasal edema is expected after prolonged sx (esp if the head was below the level of the heart)
What is considered norm in the CV system for equine
- 2 degree AV block is gen norm & is due to inherently high vagal tone
What are some CV consideration
- Have a large SA node, so a wander pacemaker (variations in the shape of the P Waves) is common
- May see biphasic P wave
- B/C atrial mass they are predisposes to re-entrant rhythms (the most common is atrial fibrillation w/ it irregularly irregular pattern)
Describe using acepromazine for pre med
- Used as an adjunt to other sedatives in an excitable horse
- Caution when used in the breeding stallions due to the potential for penile prolapse
- Not typically used alone
Describe using alpha 2 agonist for pre med
- Xylazine & detomidine most common
- Starting to use dexmedetomidine (most for CRI)
- Most common used for sedation, muscle relaxation, & analgesic properties
- Look @ the duration & onset of action to see which one would be better for the procedure
Describe using opioids for pre med
- Likely to cause excitement w/ co admined w/ alpha 2 agonists or ace
- Which one to use is limited to the cost
- Butorphanol is common but has very weak analgesia
- Most side effect or concern is slowing down of the GI tract
Describe using benzodiazepines for pre med
- Rarely admined by itself except in foals
- Use mostly w/ ketamine
- Can cause excitment
Describe ketamine for IV induction
- Ketamine + benzo to help decrease ketamine muscle rigidity
- Can use ketamine + guaifenesin
- Ketamine alone can be used following after a heavy alpha 2 agonist
- Can cause apneustic (holding breath) breathing pattern
Describe propofol for IV induction
- Not commonly used
- Need a large vol
- Poor quality induct
Describe telazol for IV induction
- Smooth induction
- Rough recovery
- Given after alpha2 agonist sedation
Describe alfaxalone for IV induction
Very expensive
What is the MAC of isoflurane in equine
1.31%
What is the MAC of sevoflurane for equine
2.31%
What is gen needed to prevent movement during sx
Need to maintain end tidal concentration of inhalant about 30% greater than MAC
Describe triple drip (TIVA)
- Recipe in pic
- There is twice as much ketamine than xylazine
- Can use for up to 1 H
- No more than an hour b/c GG can cause them to become to weak/wobbly in recovery
- > 15% can lead to irritation of BV
- Can possibly use other alpha 2 agonist (detomidine or medazolam)
What are some adjunt drugs we can add
- Lidocaine CRI to improve analgesia & GI motility b/c is reduces mac by 25%
What is the diff in LA ax machines
- Have mechanical ventilators built in
- Just bigger in gen
- Has all the sam components
Describe equipment used in equine ax
- Scavenging should usually be active b/c canisters become ineffective @ high fresh gas flow rates
- Hydraulic lift w/ protective padding & soft ropes
Describe the induction period
- Designated space
- Owner kept @ a safe distance & explain
- Keep the noise level down
- Be sure the px is adeq sedated (They should not be excited)
- Blind intubation can be performed in lateral or in sternal recumbency
- Will need a mouth gag
What should the placement of the head be when doing induction in a stall w/ a swing gate
- Keep head steady until they buckle
- Then push the head up to make the horse “dog sit”
What should the placement of the head be when doing free fall induction
Once the horse begins to buckle & relax turn the head the OPPOSITE direction of how you want the horse to lay
Do you need to tie in the ETT
No
Describe maintenance w/ TIVA
Px ideally intubated on oxygen
Describe maintenance w/ inhalant ax
- Higher O2 flow rate & vaporizer setting in the beginning
- Once adeq plane of ax is reached reduce the vaporizer & oxygen setting to maintenance levels (5-10 mL/kg/min)
What are some physical signs of ax depth
- Eye signs - palpebral, will have corneal reflexes, lacrimation, nystagmus, & Position of the eyeball
- Muscle tone & movement of the limb
- Swallowing
- Ear movement
- Anal sphincter tone
- Response to surgical stim
- Shivering & stretching
- RR, HR, & BP are less reliable
